Vertical Order Traversal of Binary Tree Nodes

bloomberg Given a binary tree, return the vertical order traversal of its nodes' values. For each node, its horizontal distance defines its position in the vertical column. In the same column, the priority is determined by depth and from left to right. In a binary tree, the nodes have unique identifiers. Implement a function to get the list of nodes' values in vertical order traversal. Example Input [3,9,20,null,null,15,7]